Carbonate-rich Pleistocene through upper Paleocene sediments were recovered at Site 1263, with a clay layer marking the lowermost Eocene. Variably preserved nannofossils are present in all samples. Slight dissolution and overgrowth of discoasters are common. Planktonic foraminifers generally show good preservation, but fragmentation occurs across the E/O boundary interval and severe fragmentation and a barren sample were observed in the lowermost Eocene. Benthic foraminifers are rare in almost all samples and show generally good preservation, but dissolution and fragmentation occur in the lowermost Eocene. Benthic and planktonic foraminifers in Cores 208-1263A-38X through 40X (373–401 mcd) contain recrystallized or filled-in specimens.
Shipboard examination of calcareous nannofossils and planktonic foraminifers permitted preliminary zonal and stage assignments (Fig. F22; Tables T5, T6, T7, T8). Biochronological ages plotted against mcd delineate overall sedimentation rates (Fig. F23) (see "Age Model and Mass Accumulation Rates"). Most of the Miocene and the upper Oligocene are not represented because of unconformities; the upper and uppermost middle Eocene are condensed, but the lower Eocene through upper Paleocene is expanded. Benthic foraminifers indicate upper abyssal depths (2000–3000 m) for the site from the middle Eocene through Pleistocene. The paleodepth could not be ascertained for the early Eocene, and it was middle lower bathyal (~1500 m) during the late Paleocene through Pleistocene (Table T9).
Calcareous nannofossil assemblages were examined in core catcher and additional samples for selected intervals of all holes. Depth positions and age estimates of key biostratigraphic markers are shown in Table T5; a distribution chart for the core catcher samples is shown in Table T6.
Nannofossils are present throughout the section and have moderate to good preservation except in a 5-cm-thick interval just above the P/E boundary, where only a few solution-resistant taxa are present. Discoasterids are generally affected by overgrowth, which prevents the recognition of some species, mainly in the Eocene.
Core 208-1263A-1H is placed in the Pleistocene, and the interval from Cores 208-1263A-2H through Sample 4H-1, 50 cm, is placed in the Pliocene. Samples 208-1263A-4H-1, 80 cm, through 4H-6, 100 cm, contain upper and middle Miocene assemblages. Lower Miocene nannofossils (of Subzone CN1c and Zone NN2) are present in Section 208-1263A-4H-CC, suggesting that there is an unconformity between these samples.
Lowermost upper Oligocene and lower Oligocene sediments were recovered in Cores 208-1263A-6H through 10H and 208-1263B-1H through 4H. The nannofossil assemblages show signs of slight dissolution and generally low diversity, but the Oligocene markers Sphenolithus ciperoensis and Sphenolithus distentus are present. These small sphenoliths show variable abundances and are rare or have discontinuous distributions in some intervals. Although their lowermost occurrences are not distinct events at many locations (Olafsson and Villa, 1992), at Site 1263 we could recognize the lowermost occurrences (bottom [B]) of S. ciperoensis and S. distentus, which define the boundaries of Subzone CP19a and Zone CP18, respectively. Among the other Oligocene sphenoliths, Sphenolithus predistentus is consistently present, whereas Sphenolithus pseudoradians occurs sporadically and in low abundances in the upper part of its range (Cores 208-1263A-8H and 9H). Key elements of lower Oligocene assemblages such as Reticulofenestra spp., Dictyococcites spp., and Cyclicargolithus spp. are common to abundant, whereas representatives of the genus Helicosphaera are absent in most of the Oligocene, with the exception of Helicosphaera compacta. The zonal boundaries CP17/CP16c (NP23/NP22) and CP16c/CP16b (NP22/NP21) occur between Sections 208-1263A-8H-4 and 8H-5 and in Section 208-1263A-9H-4, respectively.
The succession of nannofossil events that characterizes the Eocene–Oligocene transition was recognized in Cores 208-1263A-9H through 11H and 208-1263B-4H and 5H. The boundary between Subzones CP16c and CP16b (NP22/NP21) and the uppermost occurrence (top [T]) of Ericsonia formosa is distinct. In Zones NP22 and NP21, Isthmolithus recurvus is rare and occurs discontinuously. In Zone NP21 (CP16b+a), an increase in the relative abundance of Ericsonia obruta approximates the E/O boundary. Common to abundant E. obruta occurs in a short interval in Sections 208-1263A-9H-5 and 10H-3, corresponding to the basal Oligocene. Among the rosette-shaped discoasters, the T of Discoaster barbadiensis, which together with the T of Discoaster saipanensis defines the boundary between Subzone CP16a and Zone CP15 (NP21/NP20), was difficult to locate because the species is rare and occurs discontinuously in the upper part of its range. The T of D. saipanensis in Cores 208-1263A-11H and 208-1263B-5H places sediments below these levels in the uppermost Eocene.
Highly diverse calcareous nannofossils are present throughout the Eocene. Major components of the assemblages are Chiasmolithus spp., Coccolithus eopelagicus, Dictyococcites spp., Discoaster spp., Ericsonia spp., Reticulofenestra umbilicus, Reticulofenestra dictyoda, Sphenolithus spp., and Zygrhablithus bijugatus. Overgrowth affects the solution-resistant taxa (e.g., Discoaster species and the middle Eocene markers Nannotetrina spp.) and sometimes hampers their identification. Most of the Eocene zonal boundaries could be recognized (Fig. F22), with the exception of the upper middle Eocene Subzone CP14b/CP14a (NP17/NP16) boundary and the upper lower Eocene Zone CP11/CP10 boundary. The marker for the first of these boundaries (P14b/CP14a; Chiasmolithus solitus) was not recognized because of preservation problems, and we used the B of Dictyococcites scrippsae to approximate this boundary. As for the second boundary (CP11/CP10), its marker species Toweius crassus is present in older sediments in the CP9b zonal interval and the species is thus not reliable. Three nannofossil events (the B of D. scrippsae, the B of Dictyococcites bisectus, and the T of Chiasmolithus grandis) characterize upper middle Eocene Zone NP17, which has a duration of 3.2 m.y., and they all occur in Core 208-1263A-7H, suggesting that this interval is condensed.
The lower Eocene (Cores 208-1263A-22H through 32H and 208-1263B-13H through 26X) assemblages are characterized by abundant Tribrachiatus orthostylus, common Sphenolithus radians, and discoasters (e.g., Discoaster lodoensis, Discoaster diastypus, and Discoaster multiradiatus).
Specimens of the Rhomboaster-Tribrachiatus plexus belonging to the species Tribrachiatus contortus and preceding the lowest occurrence of the lowermost Eocene marker T. orthostylus have rare and scattered occurrences in Cores 208-1263A-29H through 32H and are poorly preserved because of recrystallization. Therefore, the boundary between Subzones CP9b and CP9a (NP11 and NP10) could not be confidently recognized and it is placed tentatively at the lowermost occurrence of S. radians. In the sediments just above the benthic extinction event (BEE) (Sections 208-1263A-33X-2 through 34X-1), common specimens of Rhomboaster cuspis and Rhomboaster calcitrapa are present and provide a distinct nannofossil biostratigraphic signal. As observed at Site 1262, the genus Fasciculithus shows a distinct distribution pattern in its final range, with a decrease in abundance coincident with the increase of Z. bijugatus (between Samples 208-1263A-33H-2, 110 cm, and 13H-2, 126 cm), just above the BEE. The genus Fasciculithus has its uppermost occurrence in Cores 208-1263A-32H and 208-1262B-27X.
Paleocene assemblages belonging to the biostratigraphic interval from Zones CP8 through CP4 (NP9–NP5) are present in the lower part of the sedimentary record (Cores 208-1263A-35X through 40X, Cores 208-1262B-30X through 32X, and Sections 208-1262C-14H-CC through 16X-CC). Nannofossils are generally diverse and moderately preserved. Common Discoaster taxa (D. multiradiatus, Discoaster nobilis, and Discoaster mohleri) characterize the upper part of the Paleocene interval. Other important components of the assemblages are Toweius spp., Coccolithus pelagicus, Prinsius spp., Chiasmolithus spp., Cruciplacolithus spp., Heliolithus spp., and Ericsonia spp. All the key elements for the biostratigraphic classification of this time interval were recorded, and the boundaries between upper Paleocene Zones CP8 through CP4 (NP9–NP5) were recognized (Fig. F22).
Examination of core catcher samples revealed that planktonic foraminifers are abundant and generally well preserved throughout much of the section, although specimens display signs of diagenetic alteration in the lowermost part of the cored section (upper Paleocene). Additional samples were taken through a short stratigraphic interval that contains the P/E boundary interval in Hole 1263A. Shipboard examination of the assemblages facilitated preliminary determination of the stratigraphic ranges for various taxa (Table T8).
Section 208-1263A-1H-CC (2.06 mcd) contains a typical Pleistocene temperate water fauna. Common species are Globorotalia crassaformis, Globorotalia truncatulinoides, Globorotalia tumida, Globoconella inflata, Globigerinoides ruber, Globigerinoides sacculifer, Globigerinella siphonifera, Hirsutella scitula, and Neogloboquadrina pachyderma (dextral). The base of Subzone Pt1a (~2.02 Ma), used to approximate the Pliocene/Pleistocene boundary, is placed between Sections 208-1263A-1H-CC and 2H-CC at an estimated depth of ~7 mcd.
The T of Sphaeroidinellopsis seminulina falls between Sections 208-1263A-2H-CC and 3H-CC, indicating that the base of the lower Pliocene Zone PL4 (3.18 Ma) is at ~18 mcd. The presence of Paragloborotalia kugleri, Globoquadrina dehiscens, and Catapsydrax dissimilis in Section 208-1263A-4H-CC indicates an early Miocene age for that sample (Subzone M1b). Thus, an unconformity at ~29 mcd separates lower Pliocene from lower Miocene sediments.
Poor core recovery and reworking precluded recognition of the Oligocene/Miocene boundary. Core 208-1263A-5H is mostly barren, but Section 208-1263A-5H-CC (34.54 mcd) contains P. kugleri, which places this assemblage in the lowermost Miocene (Zone M1). Mixed with this lower Miocene assemblage, however, are Oligocene taxa (e.g., Globigerina angulisuturalis and Chiloguembelina cubensis), indicating extensive reworking. Moreover, Section 208-1263A-6H-CC (56 mcd) yields an upper–lower Oligocene assemblage (P20) that contains characteristic species such as C. cubensis, Paragloborotalia opima, Globoquadrina venezuelana, Globigerina euapertura, and Globigerina ciperoensis. Sections 208-1263A-7H-CC (68 mcd) and 8H-CC (79 mcd) are assigned to Zone P19 based on the presence of rare "Globigerina" ampliapertura.
The E/O boundary interval is in Cores 208-1263A-9H through 11H. The presence of species of the genus Pseudohastigerina and the absence of typical late Eocene taxa places Sections 208-1263A-9H-CC (90 mcd) and 10H-CC (100 mcd) in Zone P18, the lowermost zone of the Oligocene. The assemblage in Section 208-1263A-10H-CC is heavily fragmented and contains numerous hantkeninid spines that have been reworked up into the lowermost Oligocene. Section 208-1263A-11H-CC (110 mcd) is assigned to the upper Eocene (Zones P15–P16) and is best described as a "Globigerinatheka sand." The scarcity of other taxa in this sample reflects intense dissolution and/or sorting.
The overall absence of several key tropical marker species due to the location of the site in a temperate region reduced the level to which the Eocene could be biostratigraphically subdivided. Section 208-1263A-12H-CC (118 mcd) straddles the upper/middle Eocene boundary and is assigned to Zone P15 based on the presence of Turborotalia cerroazulensis, Turborotalia cerroazulensis cocoaensis, and Globigerinatheka semiinvoluta and the absence of morozovellids and acarininids. The base of Zone P15 is placed at 124 mcd (between Sections 208-1263B-6H-CC and 7H-CC), as indicated by the co-occurrence of Acarinina spp. and T. cerroazulensis cocoaensis.
The absence of Orbulinoides beckmanni hinders differentiation of Zones P12, P13, and P14, and Sections 208-1263A-14H-CC through 16H-CC (142–167 mcd) are thus loosely assigned to Zones P12–P14. Taxa common to these Hantkenina spine-bearing assemblages are Acarinina spinuloinflata, Acarinina bullbrooki, Acarinina crassata, small Morozovella spinulosa, and Globigerinatheka spp.
Only two specimens of Morozovella aragonensis are found in Section 208-1263A-17H-CC (177 mcd), marking the uppermost occurrence of this species. Consequently, Sections 208-1263A-17H-CC and 18H-CC are assigned to Zone P11. The relative abundance of M. aragonensis increases downhole in Sections 208-1263A-18H-CC through 26H-CC (187–270 mcd). The absence of such dissolution-susceptible marker species as Hantkenina nuttalli and Planorotalites palmerae hampers differentiation of Zones P9 and P10, the boundary of which demarcates the middle/early Eocene boundary. We substituted a downhole reduction in globigerinathekid diversity and concomitant increases in the relative abundances of Morozovella caucasica, Subbotina higginsi, and "Globigerinatheka" senni as alternative biostratigraphic indexes. Using these criteria, we tentatively place the middle/lower Eocene boundary in Section 208-1263A-19H-CC at 199 mcd. Sections 208-1263A-20H-CC through 23H-CC (210–240 mcd) are assigned to Zone P9 based on the presence of common, well-developed morphotypes of M. caucasica.
The absence of the marker taxon P. palmerae prevents the distinction between Zones P8 and P9. Thus, a downhole decrease in the relative abundance of M. caucasica is used to tentatively assign Sections 208-1263A-24H-CC and 25H-CC (252–256 mcd) to Zone P8. Section 208-1263A-26H-CC is assigned to Zone P7 based on the co-occurrence of M. aragonensis and extremely rare Morozovella formosa. Sections 208-1263A-27H-CC through 31H-CC (281–318 mcd) are ascribed to Zone P6. Common taxa in these P6 assemblages are Morozovella subbotinae, Morozovella gracilis, Morozovella marginodentata, Morozovella aequa, Acarinina soldadoensis, Acarinina coalingensis, "large biserial" taxa, Igorina broedermanni, Subbotina spp., and Globanomalina planoconica. Rare specimens of Morozovella velascoensis are present in Section 208-1263A-32H-CC (330 mcd), indicating that the Zone P5/P6 boundary is at ~324 mcd.
Preservation steadily declines downhole through the lowermost Eocene. Planktonic foraminifer shell sizes decrease as levels of shell fragmentation increase between Samples 208-1263A-33H-2, 108 cm, and 34X-1, 2 cm. Preservation continues to decline downhole until Sample 208-1263A-34X-1, 27 cm (~335.61 mcd), which is barren. The base of this clay-rich interval is correlative with the BEE at the P/E boundary (~335.66 mcd). Below this clay-rich interval (Samples 208-1263A-34X-1, 37 cm, through 124 cm), preservation improves and abundant large planktonic foraminifers are present. Assemblages from below the P/E boundary are composed of taxa such as M. subbotinae, M. aequa, M. velascoensis, Morozovella occlusa, Subbotina velascoensis, G. planoconica, A. soldadoensis, and A. coalingensis.
The oldest sediments recovered from Site 1263 are of the upper Paleocene Zone P4 (~57.1 Ma). The Zone P4/P5 boundary is delimited by the T of Globanomalina pseudomenardii (55.9 Ma) at ~351 mcd, and Zone P4 extends downsection from Sections 208-1263A-36X-CC through 40X-CC. Preservation declines through this interval, with specimens exhibiting chalky infilling and signs of recrystallization. Assemblages in this interval are composed primarily of G. pseudomenardii, G. planoconica, M. velascoensis, Morozovella acutispira, Morozovella conicotruncata, Morozovella angulata, Acarinina mckannai, Acarinina subsphaerica, Acarinina nitida, and assorted igorinids and subbotinids.
All core catcher samples from Hole 1263A were semiquantitatively investigated for benthic foraminifers. In addition, samples were studied from intervals in Holes 1263B and 1263C (which were not recovered in Hole 1263A) and across the P/E boundary in Holes 1263A and 1263C (Table T9).
In most samples, benthic foraminifers are outnumbered by planktonic foraminifers, with the exception of those in the lowermost Eocene in which the assemblages have suffered strong dissolution. Preservation is generally good, with the exception of samples with strong dissolution in the lowermost Eocene and samples from the lowermost three cores, where specimens are recrystallized and filled in (Sections 208-1263A-38X-CC and 40X-CC; 391–401 mcd).
Benthic foraminiferal assemblages from Site 1263 indicate deposition at upper abyssal depths (2000–3000 m) in samples from above 234 mcd (Sections 208-1263A-1H-CC through 22H-CC). Paleodepths could not be estimated for Section 208-1263A-23H-CC through Sample 34X-1, 27–28 cm (241–336 mcd; lower Eocene), because benthic foraminifers are not reliable depth indicators during that period (Müller-Merz and Oberhänsli, 1991). Samples below 336 mcd were deposited at middle lower bathyal depths (~1500 m).
Sections 208-1263A-1H-CC through 3H-CC (2–21 mcd) contain assemblages with common Globocassidulina subglobosa, Cibicidoides wuellerstorfi, Cibicidoides mundulus, Oridorsalis umbonatus, and Pyrgo spp., with varying relative abundances of the Uvigerina peregrina group, Pullenia spp., and minor Osangularia culter, Bulimina rostrata, Bolivinita pseudothalmanni, Gyroidinoides spp., Siphonodosaria spp., Nuttallides umbonifera, and Epistominella exigua. At present, similar assemblages occur along Walvis Ridge at water depths between ~2000 and 3300 m (Schmiedl et al., 1997). At these depths, bottom waters are derived from northern sources (North Atlantic Deep Water).
Assemblages in Sections 208-1263A-4H-CC through 6H-CC (35–56 mcd) resemble the assemblages in the shallower samples but lack C. wuellerstorfi and mainly contain long-lived abyssal to lower bathyal taxa such as Cibicidoides spp., O. umbonatus, Pullenia spp., and Siphonodosaria spp.
Sections 208-1263A-7H-CC through 11H-CC (69–110 mcd) contain typical upper abyssal upper Eocene through lower Oligocene assemblages including Bulimina semicostata, Bulimina elongata, C. mundulus, O. umbonatus, Gyroidinoides spp., Anomalinoides spissiformis, Nonion havanense, and common Siphonodosaria spp. as well as unilocular, laevidentalinid, and pleurostomellid taxa and rare N. umbonifera and Vulvulina spinosa. Section 208-1263A-10H-CC (100 mcd) has abundant large-ribbed Orthomorphina spp., indicative of downslope transport.
Sections 208-1263C-1H-CC through 208-1262A-22H-CC (113–234 mcd) are species rich and are characterized by the presence of abundant very large specimens of Nuttallides truempyi and large B. semicostata, Cibicidoides praemundulus, and (as in the assemblage above) O. umbonatus, Gyroidinoides spp., A. spissiformis, N. havanense, common Siphonodosaria spp. as well as unilocular, laevidentalinid, and pleurostomellid taxa. Section 208-1263C-1H-CC (113 mcd) has abundant large Orthomorphina spp., indicative of downslope transport, as well as some specimens of Plectofrondicularia paucicostata that (as Plectofrondicularia lirata) have been recorded from the upper Eocene at several South Atlantic DSDP sites to the east and west of the Mid-Atlantic Ridge over a large depth range (Tjalsma, 1983; Clark and Wright, 1984).
Section 208-1263A-23H-CC through Sample 34X-1, 27–28 cm (241–336 mcd), contain assemblages that are less species rich, as is typical for the lower Eocene in the South Atlantic Ocean over a large depth range (Clark and Wright, 1984; Müller-Merz and Oberhänsli, 1991; Thomas and Shackleton, 1996). These assemblages are characterized by the presence of Aragonia aragonensis and small smooth-walled species of Abyssamina and Clinapertina, small smooth-walled buliminid species (e.g., Bulimina kugleri and Bulimina simplex), and small specimens of N. truempyi, A. spissiformis, and N. havanense. Tappanina selmensis and Siphogenerinoides brevispinosa are rare, as are specimens of unilocular, laevidentalinid, and pleurostomellid taxa. In the lowermost part of this interval (Samples 208-1263A-33H-2, 124–125 cm, through 34X-1, 27–28 cm [334.84–335.61 mcd]), species richness is extremely low and long-lived unilocular and laevidentalinid taxa are absent. Similar assemblages have been described from immediately above the P/E BEE on Walvis Ridge (Müller-Merz and Oberhänsli, 1991; Thomas and Shackleton, 1996).
The BEE occurs between Samples 208-1263A-34X-1, 27–28 cm (335.61 mcd), and 34X-1, 37–38 cm (335.71 mcd); Samples 208-1263B-28X-CC, 38–30 cm (335.09 mcd), and 29X-1, 1–2 cm (342.86 mcd); and Samples 1263C-14H-2, 144–145 cm (335.65 mcd), and 14H-CC, 3–4 cm (335.74 mcd). Samples immediately above the lithologic contact of clay-rich material over carbonate-rich material are almost barren but contain minute specimens of N. truempyi, T. selmensis, O. umbonatus, B. kugleri, B. simplex, and Abyssamina quadrata; most are dominated by N. truempyi.
Samples below the BEE through the bottom of the hole (336–401 mcd) contain typical extremely species rich Paleocene lower bathyal through abyssal assemblages including Stensioeina beccariiformis, Aragonia velascoensis, Paralabamina lunata, Paralabamina hillebrandti, Pullenia coryelli, large thick-walled species of Gyroidinoides such as Gyroidinoides beisseli, Gyroidinoides globosa, and Gyroidinoides quadrata, and large agglutinant taxa (e.g., Clavulinoides spp., Marssonella oxycona, and Gaudryina pyramidata). In contrast to Site 1262, lower bathyal indicator species such as Alabamina creta, Bolivinoides delicatulus, Coryphostoma midwayensis, and Neoflabellina semireticulata are present, indicating middle lower bathyal depths (~1500 m).